Hammond’s remarks suggest a “substantive” referendum campaign could be launched in the spring of 2016 before a vote in the summer or autumn of that year. He said the referendum could be held next year as he confirmed that a parliamentary bill authorising it will make clear that the vote must be held by 31 December 2017. The bill is to be published on Thursday.

In regards negotiations with Europe, Hammond said ministers had been advised by government law officers that they will need treaty change for the prime minister’s plans to bar EU migrants from claiming out of work benefits and to prevent them from claiming in-work benefits for four years. “That is the best legal advice that we are receiving,” he said.

The foreign secretary told BBC Radio 4’s Today programme that Cameron, who is visiting The Hague, Paris, Warsaw and Berlin, will make clear that British voters will decide to leave the EU unless most of his demands are met.

Hammond said: “We are at the very beginning of a process here. We have a clear set of requirements. The prime minister is very clear in dealing with EU counterparts: that if we are not able to deliver on these big areas of concern that the British people have, we will not win the referendum when it comes. We expect our EU partners to engage with us in delivering a package that will enable the British people to decide that they think Britain’s future is best delivered inside the EU.”

The prime minister is planning to demand change in four broad areas. He wants to:

Bar unemployed EU migrants from claiming benefits and force EU migrants in work to wait four years before claiming in-work benefits. This will be resisted in Warsaw

Hand the UK an optout from the “ever closer union” declaration

Ensure that EU member states outside the eurozone, such as the UK, could not have changes to the rules of the single market imposed on them by eurozone countries

Give national parliaments the right to club together to block new legislative proposals.

Hammond said he expected some of Britain’s 27 EU partners to adopt hardline tactics but suggested that they would eventually work towards a deal, but he added: “We we are very confident that over the course of the summer and perhaps onwards through the winter we will be able to negotiate a substantial package of reform, which will address the concerns that the British people have and which the prime minister has articulated.”

The foreign secretary said the government wants to set a pace for the negotiations to ensure they succeed rather than rushing to secure a deal. “We are in the hands of our counterparts in the EU,” he said. “I would like to get on with it, I would like to see us making progress, but in the bill we are presenting to parliament today we have set 31 December 2017 as the last possible date for a referendum.

“Of course I would hope we can get a substantial package of reform agreed much sooner than that and then we can have a substantive referendum campaign where both sides of the argument will be able to be properly aired and properly debated before we have the vote.

“I would urge people not to speculate on an early date. We are absolutely clear that we have to get this right. We certainly are not going to trade substantive reform just for getting it done quickly. We have to get this done properly.”

The prime minister meets his Dutch counterpart, Mark Rutte, over lunch in The Hague on Thursday, followed by talks in Paris with the French president, François Hollande. On Friday, he visits the Polish prime minister, Ewa Kopacz, in Warsaw before flying to Berlin for talks with Angela Merkel, the German chancellor.

The tour comes after the government unveiled its principle measure in the Queen’s speech – a bill to permit the first referendum on Britain’s membership of the EU since 1975. The document will confirm that the government has accepted the advice of the Electoral Commission on the referendum question.

Voters will be asked: should the United Kingdom remain a member of the European Union? This contrasts with the question in the Tory private members’ bill in the last parliament which asked: do you think that the United Kingdom should be a member of the European Union? The commission suggested this question risked confusing some voters who might not have realised that the UK is already a member of the EU.

The question means that the campaign to stay in the EU will be the yes side while the campaign to leave will be the no side.

The foreign secretary’s disclosure that Britain will require treaty change for EU migrant benefit changes highlights the immense challenge of the negotiations.

As he prepared for his EU tour, Cameron was warned of the challenges ahead when the French newspaper Le Monde reported over the weekend that Hollande and Merkel have agreed reforms to the eurozone should be delivered under the EU’s current treaties.

The decision means that Cameron is unlikely to secure the “full-on” treaty change he demanded in January. British sources have suggested recently that he might press for a legally binding protocol. This could be attached to a future revision of the Lisbon treaty or to the next accession treaty for a new EU member state.